linux-kernel - Re: [patch] honour MNT

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Date:	Sun, 8 Oct 2006 12:39:42 +0200
From:	"Jesper Juhl" <jesper.juhl@...il.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Stas Sergeev" <stsp@...et.ru>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Jakub Jelinek" <jakub@...hat.com>,
	"Arjan van de Ven" <arjan@...radead.org>,
	"Linux kernel" <linux-kernel@...r.kernel.org>,
	"Hugh Dickins" <hugh@...itas.com>,
	"Ulrich Drepper" <drepper@...hat.com>
Subject: Re: [patch] honour MNT_NOEXEC for access()

On 08/10/06, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
[snip]
> Also, I guess there's the general question of what the noexec mount flag
> really means?  Does it mean "make the execve syscall fail", or does it
> mean "no bits on this filesystem may be interpreted as instructions".
> The former is simple to implement, but probably not very useful; the
> latter is not possible to implement in general.
>

As I see it, what we can resonably do with 'noexec' is
- make execve() fail.
- make access(), faccessat() return EACCESS for files stored on
'noexec' filesystems.
- make mmap(...PROT_EXEC...) fail for files stored on 'noexec' filesystems.

For things like /dev/shm we can additionally let 'noexec' mean "don't
allow executable shared memory".

Since we can't really prevent things like perl/php/bash/tcl/whatever
scripts from being executed/interpreted from there with this
mechanism, let's not worry about that.  Leave that for things like
SELinux to deal with.

I don't think we can do much more with 'noexec'.


-- 
Jesper Juhl <jesper.juhl@...il.com>
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